The present invention relates to an automatic shutter driving device adapted to be energized when the image of a subject or object is sharply focused (to be referred to as an "automatic shutter driving device" hereinafter for brevity) which is adapted to be mounted on equipment having the function of automatically focusing, such as an automaticfocusing camera (to be referred to as an "AF camera" and which automatically drives a shutter when a subject reaches or appears at a position at which the subject is focused sharply known as "snap-in-focusing".
Recently, there have been devised and demonstrated various cameras capable of using a plurality of interchangeable lens and equipped with a function for automatically focusing a subject (to be referred to as an "AF function" hereinafter in this specification for brevity).
A camera body for such AF camera (to be referred to as an "AF body" hereinafter is disclosed, for example, in U.S.A. patent application Ser. No. 103,311, filed on Oct. 1, 1987 by the same applicant.
When a photographic lens having the ability of performing an automatic focusing (to be referred to as the "AF lens" is mounted on the AF body, it becomes possible not only to perform automatic exposure controlled photography (to be referred to as the "AE", but also automatic focusing photography. When a conventional photographic lens without the capability of performing automatic focusing (to be referred to as a "conventional photographic lens" is mounted on the AF body, it becomes possible to perform AE photography.
To better understand of the present invention, the construction and mode of operation of the AF body mounted with an AF lens or a conventional photographic lens will be described briefly hereinafter.
FIG. 1 is a block diagram of a camera consisting of an AF body and an AF lens mounted thereon and reference numeral 101 represents the AF body.
AF body 101 comprises a control unit 105 for controlling the AF or AE function as well as other functions of a camera, an image unit 106 which serves to decide whether the image of a subject is sharply focused or out of focus and lens driving means 107 for shifting one or more lens elements within an AF photographic lens 71. In addition, the mount of the camera body 101 is provided with a plurality of electrical contacts 175a, 175b, 175c, 177, 179a, 179b and 181 used for exchanging information between the camera body 101 and the photographic lens 71 which is electrically connected to predetermined contacts disposed in the control unit 105.
An AF lens 71 which is adapted to be mounted on the above-mentioned AF body 101 is disclosed, for instance, in U.S. patent application Ser. No. 103,311 filed by the same applicant in which reference numeral 71 in FIG. 1 represents the AF lens.
With the camera having the above-described construction, light rays from a subject, part of which is transmitted through the AF lens 71, is focused at the image unit 106. In response to the information delivered from the image unit 106, control unit 105 obtains a degree of out-of-focus of the focused image and compares it with a reference value, thereby deciding whether the image of the subject is sharply focused or out of focus. In this case, the control unit 105 provides a focus-detection signal which is representative of whether the image is sharply focused or out of focus. In case of out-of-focus condition the control unit 105 obtains a distance over which one or more movable lens elements 87 must be shifted so that the image of the subject can be sharply focused. In response to the displacement thus determined, lens driving means 107 shifts one or more movable lens elements 87 to a position at which the image of the subject is sharply focused. In this case, the lens driving force of the driving means 107 is transmitted to one or more movable lens elements 87 through a driving force transmission means 89 incorporated in the AF lens 71. Other information required for AE and AF photography is exchanged between the body and the lens through predetermined electrical contacts, so that desired AE or AF photography can be accomplished.
In FIG. 1, reference numeral 73 represents a lens ROM in which is stored information inherent to the AF lens 71; and switching or selection means 83 which turns on or off the lens ROM depending upon whether the camera body has the AF function or not and which, in the case of an "OFF" state, delivers information, such as a F-number determined by transistors Tr.sub.1 -Tr.sub.3, as the inherent information of the photographic lens. Reference numeral 88 represents one or more lens elements in the photographic lens 71 which is different from the movable lens elements 87.
FIG. 2 is a schematic block diagram of a camera consisting of the AF body 101 and a conventional photographic lens mounted thereon. In FIG. 2, reference numeral 15 represents a conventional photographic lens.
In the case of an AF camera with the above-mentioned construction, an electrical signal representative of the mounting of the conventional photographic lens 15 is generated by utilizing the fact that the electrical contact 177 on the side of the AF body 101 is made into direct contact with the conventional photographic lens mount so that it becomes possible to accomplish AE photography by using the conventional lens 15.
In the above case consisting of the conventional photographic lens 15 mounted on the AF body 101, it is possible to accomplish AE photography; but there is a problem in that the AF function of the AF body is not positively utilized except to provide a focus indication.
If the camera shutter is driven or released in response to a decision signal representative of a sharply focused image of a subject (to be referred to as a "decision signal" even when the conventional photographic lens is mounted on the AF body, it is advantageous for camera users because not only macro-photography but also photography in coincidence coincident with a desired shutter release can be accomplished.